Summary Understanding the molecular and cellular mechanisms regulating the development, patterning and postnatal renewal of oral ectodermal appendages such as teeth, taste papillae and filiform papillae, and identifying stem and progenitor cell populations in these organs, is critical for developing regenerative strategies to replace missing teeth in cases of congenital absence or loss through disease; for understanding and treating disorders of taste, including those resulting from radiation therapy and small molecule anti-cancer drugs; and for delineating proliferation controls that may be dysregulated in oral cancers. The Wnt/?-catenin signaling pathway is necessary for many developmental processes and plays critical roles in the proliferation and self- renewal of adult stem cell populations. Genetic studies in mice reveal key functions for Wnt/?-catenin signaling at early stages of tooth and taste papilla morphogenesis. Signaling is activated broadly prior to the initiation of tooth and taste papilla development and gradually becomes restricted to sites of tooth and taste precursor development, ensuring correct positioning of tooth and taste organs. Based on our preliminary data, we hypothesize that proper localization of Wnt signaling requires competing activities of Wnt ligands and secreted Wnt inhibitors, and that these direct organ formation by spatially controlling the fates, movements and proliferation of oral epithelial cells. We will use live imaging of embryonic oral explants from mice expressing a fluorescent Wnt reporter transgene to ask whether genetic deletion or forced expression of Wnt inhibitor, or loss of a Wnt ligand important for tooth development, cause altered cell movements and/or patterns of proliferation. Filiform and taste papillae of the tongue are continuously renewed in adult life, and a subset of human patients with mutations in human WNT10A presents with adolescent onset of oral ectodermal defects including ?smooth tongues?. We hypothesize that Wnt10a/?-catenin signaling controls proliferation and/or survival of adult stem and progenitor cells required for renewal of taste and filiform papillae. To test this we will ask whether loss of Wnt10a in mice affects ?-catenin signaling and the proliferation, survival, or differentiation of tongue papilla progenitor cells; fate map Wnt responsive cells in the adult tongue to test whether they include self-renewing progenitors; and determine the cell autonomous requirement for ?-catenin for progenitor cell maintenance by deleting it specifically in Wnt-responsive cells. To determine whether Wnt signaling is necessary for survival of functional progenitors, we will test whether inhibition of filiform and taste papilla proliferation upon inducible transgenic expression of the Wnt inhibitor Dkk1 is reversible after removal of the inducing agent. These experiments will delineate mechanisms controlling proliferation and organ renewal in the oral cavity and will provide important information for designing regenerative strategies.